Remove un-needed swapBuffers calls in the tests. If a glReadPixels is done after a swapBuffers, it's results are often undefined. bug=angleproject:967 Change-Id: I4a99ca47624347ecbc0a5c084e93b997c92e1b31 Reviewed-on: https://chromium-review.googlesource.com/272423 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>